Airway adapters are generally used with patients being given respiratory assistance, such as patients under anesthesia, or patients on life support systems, to connect between the endotracheal tube (ET tube) and the ventilating tube of the breathing apparatus. These tubes convey breathing gases to the patient and exhaled breath away from the patient. The airway adapter is in the form of a short connector of tubular shape, and is required to make a connection between the generally very different cross sections of these two tubes. The airway adapter connected directly to the endotracheal tube is known as the ET adapter. Airway adapters also have the function of providing a demountable joint in the ventilation path, for the insertion of other tubes into the patient's lungs, and for the dispensing of medication into the pulmonary areas. This is necessary since it may be difficult to remove the ET itself from its connector port, without disturbing the patient or his treatment.
A non-invasive indication of the patient's respiratory condition can be obtained by the analysis of the exhaled breath gases. The measurement of the dynamic carbon dioxide content of the exhaled breath is known as capnography. Airway adapters with sampling ports are used to collect gas samples from the exhaled breath of patients for analysis. ET adapters are also available with a small-bore port extending into the wall of the gas flow path, to collect samples of the gas flowing in the airway, for gas analysis. Since, however, capnography measurements are generally not performed on a continuous basis, and the use of a sampling ET adapter would thus necessitate the sealing of the sampling port for most of the time, and the potential danger of bacterial growth in any debris lodged in the blind sampling tube, such sampling ET adapters are not generally used, a priori, for intubated neonatals. Furthermore, the termination of the sampling ports in the wall of the ET adapter airway is likely to cause the ingestion of secretions and liquids into the gas analyzer through the sampling line, especially during pulmonary suction procedures, when liquids could be sucked straight from the lungs into the sampling port opening. To avoid this problem, ET adapters are available with a sampling port extending into the center of the bore. This, however, interferes with the insertion of other tubes and apparatus down the ET tube.
For all of the above reasons, a generally used procedure with neonatals is not to use a sampling ET adapter on commencement of intubation, but to add an airway adapter with sampling port later, if and when required.
The accuracy of the capnographic measurement depends on the maintenance of a smooth laminar flow of the patient's breath through the airway adapter, so as to maintain the waveform of the exhaled breath. The waveform, which is the time varying level of carbon dioxide in the patient's breath, contains detail which can change with a response time of 10 to 100 msec. The exact form of the waveform, including these fast variations, provides information about the patient's respiratory state. Internal mixing of the gases or alterations in the waveform reduce the accuracy of the capnographic measurement by slowing down the response time, and hence reduce the amount or accuracy of diagnostic information extractable from the capnograph.
Airway components are typically made as plastic injection moldings, to enable production costs to be kept low. In order to ensure gas tight joins, components to be connected are generally produced with slight tapers, such that one component fits snugly into the other. Because of the comparatively wide manufacturing tolerances of such plastic parts, there is a wide spread in the closed dimensions of a joined pair of matching parts. Thus for instance, a loose-fitting ET adapter/ventilation tube connector pair will seal when one part is pushed much further into the other, than a tight-fitting pair. As a consequence of this, the amount of void volume (also known as dead space) produced in such a connection is very variable, and for a tight fitting pair, could be very considerable. The airway adapter should have minimal added void volume, both to reduce the effects of gas mixing, which would adversely affect the integrity of the waveform, and to reduce the anatomical dead space, which results in rebreathing.
Furthermore, the exhaled breath of patients always contains condensable water vapor, and can also contain a significant level of liquid or solid secretions such as mucous secretions and saliva. Such liquids can block or partially block the sampling line, causing a reduction in the pressure of the gases passing through the airway adapter into the gas analyzer. This pressure drop can cause alterations in the waveform, mixing of the gas, and alterations in the gas concentration , all of which reduce the accuracy of the gas analysis. The need for accurate analysis of the gas therefore dictates efficient separation of the gas from accompanying liquids or solids, while maintaining smooth laminar flow, and without the production of a substantial pressure drop or alteration in the gas waveform.
A number of novel designs for such airway adapters have been presented in U.S. Pat. No. 5,857,461, entitled “Multiple Channel Sample Port” to the present Applicants, and hereby incorporated in its entirety by reference. Furthermore, in the Background section of that patent are mentioned a number of other patents which describe airway adapters of other designs. However, none of the airway adapters described therein are satisfactory for use with neonatals. A major problem with neonatal patients is the very small flow involved. Thus for instance, a neonatal may typically exhale breaths of only 4 cc., while the volume of a standard adult airway adapter is 6 to 8 cc. This means that even a very small void volume can cause significant mixing of the neonatal's exhaled breaths, and inaccurate capnographic results. Furthermore, the fast breathing rate of neonatals makes a fast response time even more critical than for other patients. In addition, it is impractical to disconnect the ET tube of an intubated neonatal in order to change the ET adapter to fit the sampling device to be used. Finally, closed circuit systems which include suction are widely used, and it is impractical to break such circuits in order to insert and remove capnographic adapters as needed.
There therefore exists a serious need for a sampling airway adapter, especially for use with neonatal patients, which overcomes the drawbacks and disadvantages which hitherto available adapters show when used with such patients.
The disclosures of all publications mentioned in this section and in the other sections of the specification, are hereby incorporated by reference, each in its entirety.